Internal combustion engine with exhaust gas recycling system

ABSTRACT

An internal combustion engine and method of operating it that improves combustion efficiency, fuel economy and exhaust emission during low speed running. The engine is equipped with a relatively conventional main induction system and an auxiliary induction system having a substantially smaller cross sectional area for delivering a charge to the chambers of the engine at a high velocity to improve turbulence and combustion efficiency. A control valve arrangement is incorporated so that the idle and low speed requirements are supplied through the auxiliary induction system and the medium and higher load charge requirements are supplied primarily through the main induction system. An exhaust gas recirculating system is incorporated for reintroducing exhaust gases to the combustion chamber so as to reduce the emissions of nitrous oxide. A control arrangement is incorporated so that the exhaust gases are recirculated only at the time when the auxiliary induction system is supplying the primary portion of the charge requirements. A fuel enrichment system is also incorporated for providing a richer than normal fuel air-mixture at such time as exhaust gases are being recirculated. An arrangement is also incorporated for advancing the spark ignition at the time the exhaust gases are being recirculated and when the main induction system begins to supply a large portion of the engine charge requirements.

BACKGROUND OF THE INVENTION

This invention relates to an internal combustion engine incorporatingexhaust gas recirculation and more particularly to an improvement insuch an engine and in the method of operating it.

Recently, it has been proposed to improve the combustion efficiency,fuel economy, exhaust emission control and engine running at idle andlow loads by introducing a substantial proportion of the intake chargeunder these running conditions through a relatively small crosssectional area auxiliary induction system. As a result, the inducedcharge enters the chambers at a high velocity to generate turbulencewhich improves flame propagation and the aforenoted engine runningcharacteristics. It has also been known that the emission of nitrousoxide in the engine exhaust gases may be effectively controlled throughthe use of an exhaust gas recirculation (EGR) system. Most conventionalengines are extremely sensitive to the amount of exhaust gasrecirculation and poor running characteristics, particularly at lowspeeds are encountered with conventional engines using exhaust gasrecirculation. It has been found that the use of the auxiliary inductionsystem affords a greater EGR tolerance and furthermore simplifies thespark timing of an engine due to the offsetting acceleration of flamepropagation by the use of the auxiliary induction system and theretardation of the rate of flame propagation through the use of exhaustgas recirculation. A problem exists, however, in accurately controllingthe spark timing, exhaust gas recirculation control and the control ofthe proportion of the charge entering the chambers through the main andauxiliary induction systems.

It is, therefore, a principal object of this invention so as to providean improved internal combustion engine and method of operating it thatcontrols exhaust gas emissions, simplifies spark timing and providesgood running characteristics and efficiency.

In accordance with the features aforedescribed, it has further beendiscovered that the aforenoted running conditions can be significantlyimproved by providing an enrichened fuel-air mixture during the timewhen exhaust gas recirculation is being accomplished. It is, therefore,a still further object of this invention to provide an improved systemand method by which this may be accomplished.

SUMMARY OF THE INVENTION

A first feature of the invention is adapted to be embodied in aninternal combustion engine having a chamber of variable volume in whichcombustion occurs and main and auxiliary induction passages fordelivering a a charge to the chamber. The auxiliary induction passagehas a substantially lesser effective cross sectional area than the maininduction passage so that a charge will be delivered to the chamber at agreater velocity through the auxiliary induction than and through themain induction passage. Control valve means control the proportion ofthe charge delivered to the chamber through the respective inductionpassages. Exhaust gas recirculating means and exhaust gas recirculatingcontrol means are provided for recirculating a controlled amount ofexhaust gas back to the chamber. Means are provided for delivering anenriched fuel-air mixture to the chamber during such time as exhaustgases are being recirculated.

Another feature of this invention is adapted to be embodied in a methodof operating an engine having a chamber, main and auxiliary inductionpassages as set forth in the preceding paragraph. In accordance withthis feature of the invention, the engine is operated by recirculatingexhaust gases to the chamber during certain running conditions andproviding an enriched fuel air mixture for the chamber at such time asthe exhaust gases are being recirculated.

Another feature of this invention is adapted to be embodied in an enginehaving a chamber, main and auxiliary induction passages, and controlvalve means as set forth in the preceding two paragraphs. In accordancewith this feature of the invention, the engine is also provided with aspark timing device and means for advancing the spark timing from normalonly during such time as the exhaust gases are being recirculated.

Yet another feature of this invention is adapted to be embodied in amethod of operating an engine constructed in accordance with thatdescribed in the immediately described paragraph. In accordance withthis feature of the invention, the engine is operated by advancing thespark timing from normal during such time as exhaust gases are beingrecirculated and by immediately retarding the spark upon the cessationof exhaust gas recirculation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially schematic cross sectional view taken through aportion of a single cylinder of a multi cylinder combustion engineembodying this invention.

FIG. 2 is a graphical analysis of the exhaust gas recirculation inrelation to engine load curve of the engine shown in FIG. 1.

FIG. 3 is a graphical analysis of the spark timing in relation to engineload of the engine shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1 a portion of an internal combustion engine constructed andoperated in accordance with the features of this invention is identifiedgenerally by the reference numeral 11. The engine 11 consists of acylinder block 12 having a plurality of cylinder bores 13 in whichpistons 14 are supported for reciprocation. The construction associatedwith only a single of the cylinder bores 13 has been illustrated sinceit is believed that the principles of the invention may be readilyapparent and that those skilled in the art will readily perceive howthis invention is applied to the remaining cylinders.

A cylinder head 15 is affixed to the cylinder block 12 in any knownmanner and has a number of cavities 16 each of which cooperates with arespective one of the cylinder bores 13 and pistons 14 so as to providea chamber of variable volume in which combustion occurs. The cavities 16will at times be referred to as the combustion chamber and this term isintended to include the afore defined variable volume chamber. Maincylinder head intake passages 17 are formed in one side of the cylinderhead 15 and terminate in main intake ports 18. An intake valve 19, whichis operated in any known manner, controls the communication of the maininduction passages 17 with the chambers 16.

Exhaust passages 21 are formed in the opposite side of the cylinder head15 and extend from exhaust ports 22 in communication with the chambers16 to an exhaust manifold, indicated generally at 23. Exhaust valves 24,which are also operated in any known manner, control the communicationof the chambers 16 with the exhaust passages 21.

The engine 11 is also provided with an induction system which includesan air inlet 25 in which a vane type air flow detector 26 is provided.The detector 26 senses the air flow through the inlet 25 and provides acontrol in a manner to be described, for the amount of fuel dischargedby fuel injection nozzles 27 which serve each of the chambers 16 in amanner to be described.

The air inlet 25 supplies the intake air to an inlet 28 of an intakemanifold, indicated generally by the reference numeral 29 by means of aflexible conduit 31. A manually operated throttle valve 32 is providedin the inlet 28 for controlling the total mass flow to the chambers 16in a known manner. Downstream of the throttle valve 32, the manifold 29is provided with a plenum 33 from which individual runners 34 extend toserve each of the cylinder head main induction passages 17.

Automatically controlled throttle valves 35 are provided in each of therunners 34 so as to control the amount of charge delivered to thechamber 16 through the main intake system consisting of the runners 34,main induction passages 17 and intake ports 18. The control valve 35 isoperated by means of a lever 36 that is affixed to a shaft 37 whichrotatably supports each of the control valves 35. An actuating rod 38 ofa vacuum actuator 39 is connected to the lever 36 for rotating thecontrol valves 35. The vacuum actuator 39 is suitably supported on themanifold 29 by means of a bracket 41. As will become apparent, thevacuum actuator 39 is constructed so that the control valves 35 will beheld in a closed position until a predetermined time.

An auxiliary induction system is also incorporated for delivering themain portion of the charge to the chambers 16 during idle and low speedoperation. The auxiliary induction system includes an inlet 42 that isin communication with the main intake inlet 28 just downstream of thethrottle valve 32. Auxiliary runners 43 extend from the inlet 42 toauxiliary induction passages 44 formed in the cylinder head 15 adjacentthe main induction passages 17. The auxiliary induction passages 44terminate in auxiliary intake ports 45 which are juxtaposed to the mainintake ports 18 for discharge into the chambers 16 through the openintake valves 19. The effective cross sectional area of the auxiliaryinduction system consisting of the runners 43, auxiliary inductionpassages 44 and auxiliary intake ports 45, is substantially less thanthat of the main induction system so that a given mass flow of chargeentering the chambers through the auxiliary induction system will beflowing at a significantly greater velocity. It should be noted thatwhen the control valves 35 are closed, the intake flow is shunted to thechamber 16 through the described auxiliary induction system. The vacuumsignal for the actuator 39 is provided by means of a conduit, indicatedschematically at 46 which communicates the actuator 39 with a vacuumport 47 formed in the manifold 29 immediately downstream of the closedposition of the throttle valve 32.

The engine 11 includes an exhaust gas recirculation (EGR) system forrecirculating a portion of the exhaust gases from the chamber 16 back tothe chamber 16 under certain running conditions. The exhaust gasrecirculating system includes a first passage 48 that extends from theexhaust manifold 29 to an EGR valve, indicated generally by thereference numeral 49, which is of the well known back pressure type. Theexhaust gases are delivered from the EGR valve 49 to a conduit 51 whichcommunicates with the intake manifold 29 immediately upstream of theauxiliary induction system inlet 42. Recirculated exhaust gases will,therefore, be drawn back into the induction system for introduction tothe chambers 16 at a high velocity primarily through the auxiliaryinduction system.

The EGR valve 49 includes a first valve element 52 that is actuated by avacuum actuator 53 having a diaphgram 54 that divides the actuator 53into an atmospheric chamber 55 and a vacuum chamber 56. A spring 47 isprovided in the vacuum chamber 56 for normally biasing the first valvesection 52 to its open position. The vacuum chamber 56 receives itsactuating pressure from a port 58 formed in the intake manifold 29adjacent the upstream idle position of the throttle valve 32. A conduit59 communicates the port 58 with the vacuum chamber 56. In the idleposition the port 58 is exposed to atmospheric pressure and suchpressure acting through the conduit 59 into the chamber 56 causes thepressure in the chambers 56 and 55 to be substantially equal and thespring 57 will urge the valve element 52 to its opened position. Whenthe intake vacuum in the port 58 is low, such as when the throttle valve32 is only slightly opened, the port 58 will sense a low negativepressure which will tend to close the valve element 52.

The EGR valve 49 includes a second valve element 61 that controls thecommunication between a pressure chamber 62 upstream of the first valveelement 52 and the conduit 51. Accordingly, exhaust gases will not berecirculated unless both of the valve elements 52 and 61 are opened.

The valve element 62 is controlled by an actuator 63 that includes adiaphragm 64 which divides the actuator 63 into an atmospheric chamber65 and a vacuum chamber 66. A spring 67 is provided in the vacuumchamber 66 for normally urging the valve element 61 to its closedposition. The vacuum chamber 66 is provided with its signal by means ofa conduit 68 that communicates with a conduit 69.

The conduit 69 in turn communicates with a vacuum tank or vacuumaccumulator 71. The tank 71 is evacuated via the conduit 59 through arestriction or orifice 72. The tank 71 is also vented to the atmospherevia a variable orifice valve 73 that is controlled by the pressure inthe EGR valve chamber 72 through a conduit indicated schematically at74. The degree of restriction of the atmospheric vent 73 is increased asthe pressure in the chamber 62 is increased so as to reduce the amountof venting of the tank 71.

The operation and effect of the EGR valve 49 may be best understood byreference to FIG. 2. This figure indicates the amount of exhaust gasrecirculation on the absyssa in relation to engine load, which isrepresented on the ordinate. When the engine 11 is idling the port 58will be exposed to atmospheric pressure and the chambers 55, 56 of theactuator 53 and the chambers 65, 66 of the actuator 63 will be atsubstantially the same atmospheric pressure. The spring 57 will thenopen the valve element 52 and the spring 67 will close the valve element61. Hence there is no exhaust gas recirculation at idling.

As the throttle valve 32 is opened and the engine load increases atimmediately offidle, the port 58 will be exposed to a reduced pressurewhich is transmitted through the conduit 59 to the chamber 56. At thesame time, the pressure in the accumulator 71 will begin to decrease anda negative pressure will be exerted in the actuator chamber 66 so as tocause the valve element 61 to open. At this stage, the negative pressurein the chamber 56 is not sufficient to overcome the action of the spring57 so that the valve element 52 will still be held open. Thus, exhaustgas recirculation begins and follows the solid line curve shown in FIG.2.

As has been previously noted, the detector vane 26 controls the amountof fuel discharge from the nozzles 27 in relation to air flow. Thestructure for doing this is believed to be well known and, for thatreason, has not been described. Generally such structure includes anelectrical control circuit which is responsive to the angular positionof the vane 26. In accordance with this invention, this circuit includesa fuel enrichment device indicated schedmatically at 75 which forms apart of the complete fuel control system. The device 75 is switched, bymeans of a pressure operative switch indicated schematically at 76between a condition in which a relatively rich fuel air mixture issupplied and a condition in which a normal, relatively lean fuel airmixture is supplied. The switch 76 is responsive to the pressure in theaccumulator tank 71 and when the vacuum in the tank 71 is high (lowabsolute pressure) the richer mixture will be supplied. On the otherhand when the vacuum in the tank 71 is reduced (absolute pressure high)the switch 76 operates to provide a relatively lean, normal mixture.

Spark plugs (not shown) are provided for firing the charge in each ofthe chambers 16. The spark plugs are provided with a high voltage togenerate a spark at a timed interval by a distributor mechanismindicated generally by the reference numeral 77. The distributor 77includes a governor mechanism (not shown) of known type which advancesthe spark timing as the speed of the engine 11 increases. Also, apressure indicated generally by the reference numeral 78 is provided foraltering the spark timing in response to conditions now to be noted. Thepressure control device 78 includes a housing that is divided by meansof a diaphragm 79 into chambers 81 and 82. Springs 83 and 84 areprovided in the chambers 81 and 82, respectively. The diaphragm 79 isconnected by means of a link 85 to the distributor plate so as to retardthe spark timing at the rod 85 for pull to the left as shown in FIG. 1and to advance the timing when the rod 85 is moved to the right as shownin this figure. The pressure controlled timing provided by the device 78is superimposed upon the timing afforded by the governor mechanism ofthe distributor 77 in a known manner.

The first chamber 81 of the device 78 is in communication with thepressure of the vacuum tank 71 via the conduit 69. The chamber 82, onthe other hand, is in selective communication with the conduit 59 andaccordingly the port 58 by means of a conduit indicated schematically bythe reference numeral 86 and by means of a valve indicated generally bythe reference numeral 87. The valve 87 communicates the chamber 36 withthe conduit 59 when in a first position and vents the chamber 82 to theatmosphere through an atmospheric vent 88 when in a second position,which position is shown in FIG. 1. The valve 87 is responsive to thepressure in the tank 71 via the conduit 69 and a conduit 89. The valve87 is normally held in the position shown in FIG. 1 and is moved to theposition wherein the chamber 82 is exposed to the pressure in theconduit 59 when the vacuum in the tank 71 exceeds a predetermined level(absolute pressure falls to a predetermined value).

The chamber 82 and the actuator 39 are also selectively dumped toatmosphere pressure by means of a valve 91 which is interposed in theconduit 46 and the conduit 86. The valve 91 is normally held in a closedposition as shown in FIG. 1 and is movable to a position wherein anatmospheric vent 92 is opened in response to the existence of apredetermined negative pressure in the induction system downstream ofthe throttle valve sensed at a port 93. The port 93 is connected to thevalve 91 by means of a conduit schematically indicated at 94. As hasbeen noted, when the pressure at the port 93 falls to a preset value(manifold vacuum increases to a preset value) the valve 91 is actuatedso as to vent the line 46 and the chamber 82 to atmospheric pressurethrough the atmospheric port 92.

The vacuum tank 71 is also dumped selectively to the atmosphere by meansof a conduit 95 and time delay valve indicated generally by thereference numeral 96. The time delay valve 96 includes a spool 97 thatis movable between a closed position as shown in this figure and aposition wherein the line 95 is communicated with an atmospheric port,indicated schematically at 98. The valve spool 97 is operated inresponse to the pressure existing in a vacuum tank 99 which is chargedby means of a one way delay circuit including a check valve 101 and arestricted orifice 102, which are in parallel circuit with each otherand which are in communication with a vacuum port 103 positioneddownstream of the throttle valve 32 by means of a conduit, indicatedschematically at 104.

The arrangement of the time delay valve 96 is such that when thepressure in the tank 99 falls below a predetermined value, the valvespool 97 is moved from the position wherein the conduit 95 is blockedfrom communication with the atmospheric port 98 to a position whereinthe communication is opened and the tank 71 will be dumped toatmosphere. The operation is such that when the throttle valve 32 isclosed and the engine is in its idling condition, the tank 99 will berapidly evacuated through opening of the check valve 101 and the valvespool 97 will be moved to its closed position. When the throttle valve32 is opened, the pressure at the port 103 will increase and thepressure in the tank 99 will build up slowly due to the restrictedorifice 102. When the pressure reaches a predetermined value, at a timedelay afforded by the orifice 102, the valve spool 97 will be actuatedso as to dump the tank 71 into the atmosphere.

OPERATION

At idle the throttle valve 32 will be substantially closed and the port58 positioned so that it senses atmospheric pressure. Thus, atmosphericpressure will be present in the line 59 and the tank 71 will be atatmospheric pressure. Thus, atmospheric pressure exists in the chamber66 of the EGR valve actuator 63 and the valve element 61 will be closedso that there is no exhaust gas recirculation. At the same time, theatmospheric pressure will be sensed by the device 76 so that the device75 in the fuel control circuit will provide the lean or normal fuel airratio to the injectors 27. The valve 91 will be closed and therelatively low induction system pressure sensed at the port 47 will betransmitted to the actuator 39 so as to hold the control valve 35 in itsclosed position. Thus, all of the intake air for the chamber 16 will bedelivered at a high velocity through the auxiliary induction systemincluding the passages 43, 44 and port 45. The fuel charge will, ofcourse, be drawn in from the main induction passage when discharged fromthe nozzle 27. Because of the high velocity, combustion efficiency isimproved due to the fast flame propagation.

Since the tank 71 is at atmospheric pressure, atmospheric pressure willexist in the chamber 81 of the vacuum actuator 78 of the distributor 77.At the same time, the valve spool 87 will be in a position so that thechamber 82 exposed to the same pressure through conduit 59. Thus, thespark timing for the distributor 77 will be set by governor only.

As the load on the engine increases and the throttle valve 32 ismanually opened, the port 58 will now be positioned on the downstreamside of the throttle valve 32 and a reduced pressure will be experiencedat this port and through the conduit 59. At the same time, the pressurein the tank 71 will be charged down (tank 71 will be evacuated) throughthe restriction 72. The reduced pressure will, of course, build up at arate determined by the restriction of the orifice 72 and that of theadjustable vent 73 which is dependent upon the pressure in the EGRchamber 62.

The negative pressure existing in the chamber 66 of the EGR actuator 63will cause the valve element 61 to begin to open and exhaust gasrecirculation will follow the curve shown in FIG. 2. At this time, thenegative pressure in the chamber 56 is not sufficient so as to cause thevalve element 52 to close fully. When the engine speed and loadincreases the exhaust pressure in the chamber 62 will increase tofurther increase the restriction offered by the adjustable orifice 73 sothat the EGR curve follows that in FIG. 2. When exhaust gasrecirculation is commenced by opening of the valve element 61, thepressure responsive member 76 will also be actuated so as to shift thedevice 75 of the fuel control to its rich setting. Thus, when exhaustgas recirculation is begun, the fuel injection nozzles 27 will deliver aricher mixture than they were previously to that time.

Pressure in the tank 71 is transmitted to the chamber 81 of the actuator78 of the distributor 77. This pressure also is transmitted through theconduit 89 so as to actuate the valve spool 87 so that the line 86 andchamber 82 will be vented to the atmosphere through the port 88. Thus,the rod 85 will be shifted to the left and spark timing will be advancedso as to compensate for the reduction of burning rate due to the exhaustgas recirculation. During this phase of the operation, the spark advancewill follow the portion of the solid line curve AB in FIG. 3.

Previous to opening of the throttle valve 32, a negative pressure wasexerted through the port 103, conduit 104 and open check valve 101 so asto reduce the pressure in the tank 99 and cause the valve spool 97 to beheld so that the conduit 95 was closed from its atmospheric venting withthe port 98. However, as the throttle valve 32 is opened as increase inpressure will be exerted at the port 103 which will cause air graduallyto enter the tank 99 through the orifice 102 to cause the time delay ofthe shifting of the spool 97 to its venting position. After this timedelay has occurred, the valve spool 97 will be shifted to the left asseen in FIG. 1 and the line 69 and accordingly tank 71 will be dumped tothe atmosphere through the port 98. Upon this dumping, atmosphericpressure will be exerted in the chamber 66 of the EGR valve actuator 63and this pressure and the spring 67 will cause the valve element 61 toclose and cut off exhaust gas recirculation. Thus, it should be clearthat exhaust gas recirculation is continued for a predetermined time lagafter the throttle valve 32 is opened and the engine is accelerating.After that delay exhaust gas recycling is stopped.

At the same time that the tank 71 is dumped, the valve 87 will beshifted to the right so that the chamber 82 of the vacuum actuator 78will communicate with the line 59. The chamber 81 of this actuator isexposed to the same pressure so that the rod 85 of this actuator will beshifted to the right and ignition timing will be retarded alone the lineBC of FIG. 3 to that normally set by the governor of the distributor 77.

Simultaneously with retardation of the spark timing and discontinuanceof exhaust gas recirculation, the pressure responsive element 76 will beshifted so that the fuel control device 75 will again be returned to itsnormal lean condition.

As the throttle valve 32 continues to open, the pressure at that port 92will decrease until such a point that the valve spool 91 is shifted tothe right to vent the conduit 46 to atmosphere. At this time, theactuator 39 will be vented to atmosphere and the control valve 36 willopen so that a substantial portion of the charge to the chamber 16 willbe supplied through the main induction system rather than through theauxiliary induction system. Because of this, there will be no decreaseof volumetric efficiency and maximum power output of the engine is notsacrificed.

Upon opening of the control valves 35 by the shifting of the valve spool91, the conduit 86 and chamber 82 of the actuator 78 of the distributor77 will also be vented to atmospheric pressure. Thus, both chambers 81and 82 of this actuator will be at the same pressure and pressureoperated advance mechanism 78 is effectively disabled so that ignitiontiming is advanced along the curve D-E to compensate for the decreasedamount of turbulence in the chamber 16 and accordingly the retarded rateof combustion.

It should be readily apparent from the foregoing description that thedisclosed system provides for an automatic spark advance during theconditions of exhaust gas recirculation so as to accommodate theretarded rate of combustion. Furthermore, a richer than normal fuel airmixture is provided under these running conditions and these situationswill return to normal immediately upon discontinuance of the exhaust gasrecirculation. Various changes and modifications may be made from theinvention as described without departing from the spirit and scope ofthe invention, as set forth in the appended claims.

What is claimed is:
 1. In an internal combustion engine having a chamberof variable volume in which combustion occurs, a main induction passagefor supplying a charge to said chamber, an auxiliary induction passagehaving a significantly lesser effective cross sectional area than saidmain induction passage for delivering a charge to the chamber at asignificantly greater velocity than the main induction passage, controlvalve means for controlling the proportion of the charge delivered tothe chamber through the respective induction passages, exhaust gasrecirculating means for recirculating a portion of the exhaust gasesfrom the chamber back to the chamber, and exhaust gas recirculationcontrol valve means for controlling the amount of exhaust gasesrecirculated to said chamber, the improvement comprising means forproviding an enriched fuel-air mixture to the chamber only during suchtimes as exhaust gases are being recirculated.
 2. An internal combustionengine as in claim 1 wherein the exhaust gas recirculating means isresponsive to the control valve means for effecting exhausting gascirculation only when the major portion of the charge is delivered tothe chamber through the auxiliary induction system.
 3. An internalcombustion engine as in claim 1 further including a fuel injectionnozzel for discharging fuel into at least one of the induction passages,the means for providing the enriched fuel air mixture being effective toprovide additional fuel discharge from said fuel injection nozzle.
 4. Aninternal combustion engine as in claim 3 further including an air flowdetector for controlling the amount of fuel discharged by the fuelinjection nozzle.
 5. An internal combustion engine as in claim 4 whereinthe auxiliary induction passage has its inlet in communication with themain induction passage, the air flow detector being positioned in themain induction passage upstream of said auxiliary induction passageinlet.
 6. An internal combustion engine as in claim 1 wherein theexhaust gas recirculation control valve means and the means forproviding the enriched fuel air mixture each include pressure responsivemeans, said pressure responsive means being subjected to the samepressure.
 7. An internal combustion engine as in claim 6 wherein thepressure exerted on the pressure responsive means is induction systempressure, the control valve means including a manually operated throttlevalve positioned in one of the induction passages, the pressure beingsensed contiguous to the manually positioned throttle valve and beingupstream thereof when said throttle valve is in its ideal position anddownstream of said throttle valve when said throttle valve is in its offidle position.
 8. The method of operating an internal combustion enginehaving a chamber of variable volume in which combustion occurs, a maininduction passage for supplying a charge to said chamber, an auxiliaryinduction passage having a significantly lesser effective crosssectional area than the main induction passage for delivering a chargeto the chamber at a significantly greater velocity than the maininduction passage, control valve means for controlling the proportion ofthe charge delivered to the chamber through the respective inductionpassages, exhaust gas recirculating means for recirculating a portion ofthe exhaust gases from the chamber back to the chamber, comprising thesteps of controlling the amount of exhaust gases recirculated to saidchamber and providing an enriched fuel-air mixture to the chamber onlyduring such times as exhaust gases are being recirculated.
 9. The methodof claim 8 wherein the exhaust gas is recirculated only when the majorportion of the charge is delivered to the chamber through the auxiliaryinduction system.
 10. The method of claim 8 further including the stepof discharging fuel into at least one of the induction passages from afuel injection nozzle, the enriched fuel air mixture being accomplishedby providing additional fuel discharge from said fuel injection nozzle.11. The method of claim 10 including the step of controlling the amountof fuel discharged by the fuel injection nozzle by sensing air flow. 12.The method of claim 11 wherein the auxiliary induction passage has itsinlet in communication with the main induction passage, the air flowbeing detected in the main induction passage upstream of said auxiliaryinduction passage inlet.